1. Field of the Disclosure
This disclosure relates to auxiliary lift axle suspension systems for wheeled vehicles such as heavy duty dump trucks and trailers. More particularly, this disclosure relates to auxiliary lift axle suspension systems employing means other than inflatable bellows for selectively lowering and lifting the wheel bearing auxiliary axle of a vehicle into and out of road engagement.
2. Description of Related Art
Certain vehicles, such as heavy duty dump trucks, semi-trailers and the like, employ at least one designated wheel bearing axle suspension system capable of being raised and lowered selectively into and out of load bearing engagement with the road surface. The need to selectively lift and lower the axle usually arises in order for the vehicle to comply with maximum highway weight limit laws, though there may also be other reasons for lifting or lowering the axle (e.g., lifting the axle when traveling off-road or lowering the axle to provide an additional measure of safety when the vehicle is being loaded). These maximum weight limit laws are intended to prevent damage to roadways, particularly bridges, so they are often referred to as “bridge laws.” These bridge laws often mandate, not just a maximum vehicle weight, but further prescribe (e.g., as by the so-called “bridge formula”) that the required number of axles be spaced in such a manner so as to distribute the weight of the vehicle and its cargo over a selected length of the vehicle. The extra axles used to decrease the weight supported by each axle and their associated suspension systems are often referred to as “auxiliary” axle suspension systems. The ability to lawfully carry a greater amount of cargo often translates into increased profits and a more economically efficient use of the vehicle, so many efforts have been made to provide the most advantageous auxiliary axles.
One type of auxiliary axle which has been successfully employed incorporates a “parallelogram” lift axle suspension system. Systems of this type are described in greater detail in a variety of patent publications, including U.S. Pat. No. 5,403,031 to Gottschalk et al. and U.S. Pat. No. 6,880,839 to Keeler et al., both of which are incorporated herein by reference. Further examples of lift axle suspension systems of this type may be found in the products commercialized by Hendrickson USA, L.L.C. of Itasca, Ill.
Known lift axle suspension systems of this type typically employ a plurality of inflatable bellows, with one oriented substantially vertically and another oriented generally horizontally, as shown in FIGS. 1 and 2. The vertical bellows, which is generally indicated at R, is often referred to as the “ride spring” or “ride bellows,” while the horizontal bellows, which is generally indicated at L, is often referred to as the “lift spring” or “lift bellows.” FIG. 1 shows the ride bellows R deflated and the lift bellows L inflated, which raises the associated axle A and wheel W out of contact with the ground. FIG. 2 shows the ride bellows R inflated and the lift bellows L deflated, which brings the axle A to a lower vertical position and places the associated wheel W in contact with the ground.
While lift systems of the type illustrated in FIGS. 1 and 2 have proven to be suitable, it may be advantageous to provide a lift axle suspension system which employs a different lift mechanism. For example, it is possible for the lift bellows L to become punctured or damaged, which may prevent it from properly inflating and lifting the tire of the auxiliary axle off of the ground. Further an inflatable bellows may be relatively large and expensive and, when used in combination with an inflatable ride bellows, may increase the complexity of the associated air controls. Accordingly, it may be advantageous to provide a lift mechanism which does not rely on an inflatable lift bellows.
Additionally, if the lift bellows L becomes damaged, it is possible that debris could become expelled onto the roadway, possibly damaging the associated vehicle or another vehicle on the roadway. Accordingly, it may be advantageous to provide a lift mechanism which is mounted to the associated lift axle suspension system or otherwise configured in a way that prevents the release of debris upon damage to the lift mechanism.